A mmWave communication system has been regarded as a promising technology for the next generation of cellular systems. To compensate the large pathloss exponent of mmWave channels, a high beamforming gain is used. For the sake of the small wavelength of mmWaves, large antenna arrays can be implemented with a small antenna spacing and potentially lead to orders of magnitude increases in data rate for wireless communications. One of the inevitable limitations of such large antenna arrays, however, is significant hardware power consumption due to the large number of antenna outputs.